Electronic system adapted for passive convective cooling and staged use of electrohydrodynamic (ehd) and mechanical air movers for quiet forced convection assist

ABSTRACT

Flow paths, duct work, ventilation boundaries, and/or placement of EHD and mechanical air mover within a electronic device enclosure can all affect the efficacy of a thermal management solution that seeks to provide silent air cooling over a significant thermal operating envelope with staged introduction of electrohydrodynamic (EHD) and mechanical air mover devices. For electronic devices in which it is desirable to employ passive, unforced convective cooling over a portion of the thermal operating envelope, practical designs for consumer electronics form factors may be quite sensitive to flow path, duct work and ventilation boundary design as well as to the placement of EHD and mechanical air mover components relative thereto and to each other. A range of inventive solutions that have been developed to address some or all of these design challenges.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional Application Nos. 61/444,574, filed Feb. 18, 2011, and 61/442,166, filed Feb. 11, 2011, each of which is incorporated herein in its entirety by reference.

BACKGROUND

The present application relates to thermal management and, more particularly, to systems in which micro-scale cooling devices that generate ions and electrical fields to motivate flow of fluids, such as air, are part of a thermal management solution to dissipate heat.

Devices built to exploit ionic movement of a fluid are variously referred to in the literature as ionic wind machines, electric wind machines, corona wind pumps, electro-fluid-dynamic (EFD) devices, electrohydrodynamic (EHD) thrusters, EHD gas pumps and EHD fluid or air movers. Some aspects of the technology have also been exploited in devices referred to as electrostatic air cleaners or electrostatic precipitators. When employed as part of a thermal management solution, an ion flow fluid mover may result in improved cooling efficiency with reduced vibrations, power consumption, electronic device temperatures and/or noise generation. These attributes may reduce overall lifetime costs, device size or volume, and in some cases may improve system performance or user experience.

As electronic device designers drive to smaller and smaller form-factors, such as in the extremely thin handheld devices popularized by iPhone and iPad devices available from Apple, Inc., packing densities of components and subsystems create significant thermal management challenges. Likewise, display-oriented consumer electronics devices (whether packaged as entertainment-centric large-screen flat-panel televisions, compute-centric all-in-one computers or some amalgam of the two) can present significant thermal management challenges. As with the popular handheld devices, thinness, which can be a significant figure of merit in the marketplace, tends to exacerbate thermal management challenges. Worse still, in many cases (particularly for devices used for audio/visual entertainment), noise associated with conventional thermal management solutions can significantly detract from the user experience.

Notwithstanding the promise of EHD air mover technologies, significant practical integration challenges exist, particularly in consumer electronics devices that may seek to include both EHD and mechanical air mover technologies as part of an integrated thermal management solution.

SUMMARY

It has been discovered that flow paths, duct work, ventilation boundaries, and/or placement of EHD and mechanical air mover within a electronic device enclosure can all affect the efficacy of a thermal management solution that seeks to provide silent air cooling over a significant thermal operating envelope with staged introduction of electrohydrodynamic (EHD) and mechanical air mover devices. In particular, for electronic devices in which it is desirable to employ passive, unforced convective cooling over a portion of the thermal operating envelope, practical designs for consumer electronics form factors may be quite sensitive to flow path, duct work and ventilation boundary design as well as to the placement of EHD and mechanical air mover components relative thereto and to each other. The illustrated embodiments, depictions, and claims that follow are descriptive of a range of inventive solutions that have been developed to address some or all of these design challenges.

Passive Convective Cooling with Electrohydrodynamic (EHD) and Mechanical Air Movers for Forced Flow Assist

In some embodiments in accordance with the present invention, an electronic system includes an enclosure having inlet and outlet ventilation boundaries and a flow path defined within the enclosure between the inlet and outlet ventilation boundaries. One or more thermal sources within the enclosure generate heat during operation of the electronic system. The thermal sources are thermally coupled to heat transfer surfaces introduced into the flow path to dissipate heat through passive cooling and forced convection cooling. An EHD air mover is selectively operable to motivate air flow along the flow path for forced convection cooling of at least a portion of the heat transfer surfaces and a mechanical air mover is selectively operable to contribute to the air flow over at least a portion of the heat transfer surfaces.

In some implementations, the EHD air mover is configured to provide forced convection cooling upon detection of a first performance threshold value, and the mechanical air mover is configured to provide active cooling upon detection of a second performance threshold value. In some cases, the EHD air mover and mechanical air mover are both configured to provide forced convection cooling upon detection of a third performance threshold value. The first and second performance threshold values can characterize at least one of a temperature, loading, output, and heat generation of the one or more of the thermal sources.

In some implementations, the EHD air mover and the mechanical air mover motivate air in series along the air flow path during concurrent operation. In some implementations, the EHD air mover and the mechanical air mover motivate air in parallel over respective heat transfer surfaces.

In some implementations, the EHD air mover is positioned upstream of the mechanical air mover and the mechanical air mover includes an ozone reducing material.

In some implementations, an air flow gate is moveable to provide a lower impedance path bypassing the mechanical air mover during EHD air mover operation.

In some implementations, a lower air flow impedance is provided to flow through the EHD air mover than to flow through the mechanical air mover. For example, heat transfer fins adjacent the EHD air mover may have a wider fin pitch or lesser fin depth relative to heat transfer fins adjacent the mechanical air mover. Similarly, air flow motivated by the mechanical air mover may support increased thermal loading of respective heat transfer surfaces relative to those cooled by EHD motivated air flow. For example, dissimilar thermal loading may be accommodated between the respective heat transfer surfaces cooled by the EHD and mechanical air movers by increased thermal conductivity, e.g., using different conductive materials or different heat transfer surface dimensions.

For example, in some implementations, an integral heat transfer device can include a thicker copper portion and/or closer fin pitch adjacent the mechanical air mover and a thinner aluminum portion and/or wider fin pitch adjacent the EHD air mover. Thus, one integral heat transfer device, e.g., heat pipe, can include both aluminum and copper portions with distinct sets of fins sized, constructed and arranged to complement a corresponding EHD or mechanical air mover air flow.

In some implementations, heat fins adjacent the mechanical air mover are angled with respect to a heat pipe to accommodate an air flow direction or “angle of attack” imparted by rotation of the mechanical air mover. Variations in heat fin angle, dimension, or pitch can also accommodate variation in an air flow profile of the mechanical air mover, e.g., fan blade movement can create a higher pressured faster flow on one side of the air flow and a lower pressure slow flow at the opposite side of the air flow. In some implementations, such variation of heat transfer surfaces can be used to provide a substantially uniform or at least partially smoothed flow profile over respective areas to achieve a more uniform flow through at an outlet ventilation boundary.

Electrohydrodynamic (EHD) Air Mover and Ventilation Path that Includes Mechanical Air Mover with Flow Restriction Mitigation

In some embodiments in accordance with the present invention, an electronic system includes an enclosure having inlet and outlet ventilation boundaries. An EHD air mover is disposed within the enclosure to motivate air flow along a flow path between the inlet and outlet ventilation boundaries. Heat transfer surfaces are thermally coupled to one or more thermal sources within the enclosure that, during operation of the electronic system, generate heat. The heat transfer surfaces are introduced into the flow path downstream of the EHD air mover and include an ozone reducing surface treatment. A mechanical air mover is selectively operable to contribute to the air flow without, during periods when the mechanical air mover does not substantially contribute, substantially impeding the air flow over at least a portion of the heat transfer surfaces.

In some implementations, flow restrictions otherwise imposed by the mechanical air mover during periods when the mechanical air mover does not substantially contribute to the air flow are mitigated by providing a low-speed idle power to the mechanical air mover. In some implementations, flow restrictions of the mechanical air mover are mitigated using a bypass path. In some cases, the bypass path includes the EHD air mover.

In some implementations, the electronic system is operable in a passively ventilated mode, and the flow path is oriented to, during passively ventilated operation of the electronic system, allow unforced convective air flow upward from the heat transfer surfaces, wherein draw of replacement air is substantially unimpeded by the mechanical air mover. In some cases, in the passively ventilated mode, the unforced convective flow is drawn primarily through the EHD air mover rather than the mechanical air mover.

In some implementations, the mechanical air mover precedes the EHD air mover in the flow path. In some implementations, the mechanical air mover follows the EHD air mover in the flow path and includes an ozone reducing surface treatment on at least one of the air mover housing and the air mover blades. In some implementations, ozone reducing material is provided on various surfaces downstream of the EHD air mover, whether upstream or downstream of the mechanical air mover, e.g., on surfaces of an internal plenum, duct, heat pipe, heat spreader, and the like.

In some implementations, the electronic system further includes a valve that merges or otherwise controls respective air flow contributions of the mechanical air mover and the EHD air mover. In some implementations, the EHD air mover and the mechanical air mover direct respective air flows over separate portions of the heat transfer surfaces.

Selectively Engageable Electrohydrodynamic (EHD) and Mechanical Air Movers, Each for Motivating Air Flow Over a Separate Portion of a Unitary Set of Heat Transfer Surfaces

In some embodiments in accordance with the present invention, an electronic system includes an enclosure having inlet and outlet ventilation boundaries; and an EHD air mover and a mechanical air mover, each selectively operable and each disposed within the enclosure to motivate air flow along a flow path between the inlet and outlet ventilation boundaries. A unitary set of heat transfer surfaces is thermally coupled to one or more thermal sources within the enclosure that, during operation of the electronic system, generate heat. Air flow from the EHD air mover traverses a first subset of the heat transfer surfaces and air flow from the mechanical air mover traverses a second subset of the heat transfer surfaces at least partially distinct from the first subset.

In some implementations, the first and second subsets exhibit at least one of dissimilar fin pitch, dissimilar fin depth, dissimilar fin height, dissimilar fin material, dissimilar thickness, dissimilar angle of attack and/or dissimilar leading or trailing edge profile. In some implementations, the first and second subsets present dissimilar traversal length to respective air flows.

In some implementations, the electronic system is operable in a passively ventilated mode, and the flow path is oriented to, during passively ventilated operation of the electronic system, allow unforced convective air flow upward through at least the first subset of the heat transfer surfaces, and draw of replacement air is substantially unimpeded by the mechanical air mover. In some implementations, in the passively ventilated mode, the unforced convective flow is drawn primarily through the EHD air mover rather than the mechanical air mover.

Staged Introduction of Electrohydrodynamic (EHD) and Mechanical Air Movers to Provide Extended Silent/Quiet Operation Modes

In some embodiments in accordance with the present invention, an electronic system includes an enclosure having inlet and outlet ventilation boundaries and a flow path defined within the enclosure between the inlet and outlet ventilation boundaries. Heat transfer surfaces are thermally coupled to one or more thermal sources within the enclosure that, during operation of the electronic system, generate heat, the heat transfer surfaces introduced into the flow path to dissipate heat through passive cooling and forced convection cooling. An EHD air mover is selectively operable to motivate air flow along the flow path for forced convection cooling of at least a portion of the heat transfer surfaces. A mechanical air mover is selectively operable to contribute to the air flow over at least a portion of the heat transfer surfaces. The electronic system is operable in a first silent cooling state characterized primarily by passive cooling and in a second silent cooling state in which the EHD air mover provides forced convection cooling. The electronic system is further operable in a third cooling state in which the mechanical air mover operates, with or without the EHD air mover, at a lower capacity to provide nearly silent forced convection below about 35 dBa; and in a fourth cooling state in which the mechanical air mover is operable at a higher capacity to provide forced convection cooling below about 40 dBa.

In some implementations, forced convection cooling in the second silent cooling state is performed at below about 20 dBa and forced convection cooling in the third forced convection cooling state is performed at below about 28 dBa.

Thermal Solution Including Mechanical Fan and EHD Air Mover Disposed within Tapered Enclosure Industrial Design

In some embodiments in accordance with the present invention, an electronic system includes an enclosure that exhibits a generally planar major surface with a substantial taper in thickness from a central portion thereof toward one or more peripheral edge portions thereof. An elongate set of heat transfer surfaces are thermally coupled to one or more thermal sources within the enclosure that, during operation of the electronic system, generate heat. An EHD air mover is operable to motivate air flow along a flow path that traverses the elongate set of heat transfer surfaces and out through an outlet ventilation boundary of the enclosure. A mechanical air mover is selectively operable to boost air flow through the EHD air mover along the flow path that traverses the elongate set of heat transfer surfaces and out through the outlet ventilation boundary. The EHD air mover and the elongate set of heat transfer surfaces are positioned within the enclosure proximate at least a first one of the peripheral edge portions wherein the substantial taper provides no more than about 10 mm of thickness, and preferably no more than about 5 mm. The mechanical air mover is displaced from the EHD air mover and the elongate set of heat transfer surfaces at a position within the enclosure wherein thickness is at least two times (2×) that at the first peripheral edge portion.

In some implementations, the mechanical air mover is positioned remote from both the inlet and outlet ventilation boundaries, e.g., centrally or at least inwardly within the enclosure, to at least partially suppress noise from the mechanical air mover. Thus, more central internal positioning of the mechanical air mover can mitigate fan noise through one or both of the ventilation boundaries. Due to silent operation of the EHD air mover, it may be positioned immediately adjacent either or both of the inlet and outlet ventilation boundaries, e.g., in a configuration defining a short air flow path through the EHD air mover with localized inlet and outlet ventilation boundaries adjacent the EHD air mover. In various implementations, one or more inlet ventilation boundaries corresponding to the EHD air mover can be positioned upstream, downstream, substantially independent, or can be openable for selective contribution relative to air flow through the mechanical air mover.

In some implementations, the electronic system includes a display and orientation of the electronic system during operation places the first peripheral edge portion upward such that the flow path through the EHD air mover and the elongate set of heat transfer surfaces is generally vertical. In some implementations, the thermal sources include one or more processors of the electronic system positioned within the central portion. In some implementations, the electronic system is operable in a passively ventilated mode, and the flow path is oriented to, during passively ventilated operation of the electronic system, allow unforced convective air flow upward through the elongate set of heat transfer surfaces, wherein draw of replacement air is through EHD air mover.

Thermal Solution Including Mechanical and EHD Air Movers with Augmented Mechanical Air Flow During Cleaning of the EHD Air Mover

In some applications, in accordance with the present invention, a method of forced convection cooling includes energizing an EHD air mover disposed within an enclosure to motivate air flow along a flow path between inlet and outlet ventilation boundaries of the enclosure. The method further includes reducing power to the EHD air mover for cleaning operations and cleaning one or more electrodes of the EHD air mover. Air flow provided by a mechanical air mover is augmented during the cleaning.

In some implementations, the augmented air flow discharges from the enclosure material removed from the one or more electrodes of the EHD air mover. In some implementations, the augmented air flow provided by the mechanical air mover is of a substantially similar flow rate to combined air flow provided during operation of both the EHD air mover and the mechanical air mover. In some implementations, the cleaning is performed by at least one of heating, vibrating, and frictionally engaging the electrode.

These and other embodiments will be understood with reference to the description herein, the drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings.

FIG. 1A is a depiction of certain basic principles of electrohydrodynamic (EHD) fluid flow.

FIG. 1B is a depiction of an illustrative high voltage power supply configuration in which emitter and collector electrodes are energized to motivate fluid flow.

FIG. 2 depicts a top view of an electronic system configuration incorporating both a mechanical air mover and an electrohydrodynamic (EHD) air mover for forced convection cooling.

FIGS. 3A-B depict schematic views of parallel air flow through mechanical and EHD air movers.

FIG. 4A depicts a schematic view of parallel air flow through mechanical and EHD air movers including a gate positioned adjacent an air flow inlet.

FIG. 4B depicts a schematic view of parallel air flow through mechanical and EHD air movers including a moveable gate providing for alternate flow between the air movers.

FIG. 4C depicts a schematic view of parallel air flow through mechanical and EHD air movers having distinct downstream ducting.

FIGS. 5A-B depict schematic views of mechanical and EHD air movers arranged in series.

FIG. 6 depicts rear view of a display device incorporating forced convection cooling from both mechanical and EHD air movers.

FIG. 7A illustrates a side view of an integral computing display device having a tapered enclosure with a narrower edge-positioned EHD air mover and thicker inwardly positioned mechanical air mover.

FIG. 7B illustrates a back view of an integral computing display device including forced convection cooling via both mechanical and EHD air movers arranged in parallel and series for staged cooling.

FIG. 8 illustrates a cleaning mechanism including a drive mechanism for transiting cleaning surfaces of the cleaning mechanism in tandem along electrodes of an EHD air mover, in accordance with various implementations.

The use of the same reference symbols in different drawings indicates similar or identical items.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Basic principles of EHD fluid flow are reasonably well understood by persons of skill in the art. Accordingly, a brief illustration of ion flow using corona discharge principles in a simple two electrode system sets the stage for the more detailed description that follows.

With reference to the illustration in FIG. 1, EHD principles include applying a high intensity electric field between a first electrode 10 (often termed the “corona electrode,” the “corona discharge electrode,” the “emitter electrode” or just the “emitter”) and a second electrode 12. Fluid molecules, such as surrounding air molecules, near the emitter discharge region 11, become ionized and form a stream 14 of ions 16 that accelerate toward second electrode 12, colliding with neutral fluid molecules 22. During these collisions, momentum is imparted from the stream 14 of ions 16 to the neutral fluid molecules 22, inducing a corresponding movement of fluid molecules 22 in a desired fluid flow direction, denoted by arrow 13, toward second electrode 12. Second electrode 12 may be variously referred to as the “accelerating,” “attracting,” “target” or “collector” electrode. While stream 14 of ions 16 is attracted to, and generally neutralized by, second electrode 12, neutral fluid molecules 22 continue past second electrode 12 at a certain velocity. The movement of fluid produced by EHD principles has been variously referred to as “electric,” “corona” or “ionic” wind and has been defined as the movement of gas induced by the movement of ions from the vicinity of a high voltage discharge electrode 10.

With reference to FIG. 1B, an EHD air mover is illustrated in which emitter and collector electrodes are energized by a high voltage power supply to motivate fluid flow over heat transfer surfaces, e.g., heat fins, a heat pipe, or a heat spreader. Typically the motivated fluid is air, although in some embodiments, particular sealed enclosure embodiments, other fluids with constituents not necessarily typical of air, may be used.

With reference to FIG. 2, an electronic system 200 incorporates both a mechanical air mover 219 and an electrohydrodynamic (EHD) air mover 220 for forced convection cooling. Electronic system 200 includes an enclosure 202 housing various electronic components and/or thermal sources, e.g., a microprocessor 204, graphics unit 206, battery and/or display illumination source. A heat pipe 214 or other heat path conveys heat from the one or more thermal sources, e.g., components 204, 206, to one or more heat transfer surfaces 216 positioned within an air flow 218 motivated by either or both of a mechanical air mover 219 and an electrohydrodynamic (“EHD”) air mover.

Reference herein to a mechanical air mover or “fan” can include any mechanical means for motivating air including fans, blowers, compressors and the like, whether the air flow is motivated axially, radially or otherwise by the mechanical air mover 219. Similarly, reference herein to EHD air movers includes any combination or types of electrodes suitable to produce ion motivated air flow therebetween.

The enclosure 202 has inlet and outlet ventilation boundaries 222, 222 a and 224 and air movers 219, 220 motivate air flow 218 along flow path between the inlet and outlet ventilation boundaries 222 and 224. EHD air mover 220 is provided with a shortened low impedance air flow path for efficient EHD cooling while mechanical air mover 219 draws air along a longer, higher resistance air flow path. While mechanical air mover 219 and EHD air mover 220 are depicted as having dedicated inlets 222 and 222 a, any of a variety of air flow configurations may be provided. For example, air flow 218 may flow over a broad area of enclosure 202 or, alternatively, across a more limited channel therein, e.g., through internal plenum 212. Similarly, inlet and outlet ventilation boundaries 222 and 224 may be arranged in any suitable combination, for example, along any combination of surfaces, edges, or sides of enclosure 202. In some implementations, (not shown), plural air movers may be provided to both push and pull airflow 218 between inlet and outlet ventilation boundaries 222 and 224.

With reference to FIG. 3A, mechanical and EHD air movers 219, 220 are arranged in parallel to motivate parallel air flow over heat transfer surfaces 216. The term “parallel” as used herein refers to the respective air flow paths through the device rather than just relative positioning of the two air movers, and parallel flows need not flow simultaneously. For example, either of mechanical air mover 219 and EHD air mover 220 can be positioned proximate either the inlet or outlet of respective air flow paths to provide parallel air flow without being positionally proximate to each other.

Mechanical air movers often produce a non-uniform air flow profile. Accordingly, it may be advantageous to place EHD air mover 220 adjacent a lower pressure side of mechanical air mover air flow at outlet 224, e.g., to minimize potential for backflow through EHD air mover 220. Similarly, higher velocity portions of an air flow can be directed over portions of heat transfer surfaces having a higher thermal density, e.g., over heat fins having a higher conductivity, larger surface, greater fin length, and the like. Note that for simplicity and clarity of illustration heat pipes, heat spreaders, thermal sources and the like are not specifically illustrated, however, one of ordinary skill in art would readily appreciate how to arrange these devices for a particular system or air mover configuration.

With reference to FIG. 3B, mechanical and EHD air movers 219 and 220 provide parallel flow over heat transfer surfaces from a common inlet 222 or plenum. In some implementations, the air flow path and heat transfer surfaces 216 may be arranged to provide a passive convection “chimney” effect as hot air rises downstream of heat transfer surfaces 216 drawing air flow along the air flow path. This passive convection may be supplemented as needed with forced convection via either or both of EHD and mechanical air movers 220, 219. While mechanical and EHD air movers 219 and 220 are depicted proximate heat transfer surfaces 216 and outlet 224, one or both may be positioned remote from the heat transfer surfaces 216 and outlet 224, e.g., closer to inlet 222 to “push” rather than “pull” air flow along the flow path.

In some cases, surfaces downstream of EHD air mover 220, e.g., heat transfer surfaces 216 or duct or enclosure surfaces, may be provided with ozone reducing material to mitigate ozone levels during operation of EHD air mover 220. Ozone reducing material can be provided on any surface downstream of EHD air mover 220. Heating of the ozone reducing material can enhance ozone reduction. Accordingly, ozone reducing material may be advantageously provided on heat transfer surfaces or any number of heated surfaces. Air flow paths, internal air plenums, heat fins and the like can be configured to provide one or more ozone reducing material treated surface area, air dwell time over a given treated surface area, and heating of a given treated surface area to achieve a desired degree of ozone reduction. Any number of ozone reducing techniques may be advantageously employed to mitigate release of ozone.

With reference to FIG. 4A, parallel mechanical and EHD air movers are positioned within distinct air flow paths separated by a proportioning valve, baffle or gate 236 positioned adjacent a common air flow inlet 222A. Gate 236 can be fixed or adjustable and can serve, in some implementations, to alternately block one EHD or mechanical air mover air flow path during operation of the other of the EHD and mechanical air mover. In some cases, such gating may serve to prevent backflow through one of the air flow paths or to provide desired cooling stages.

With reference to FIG. 4B, parallel airflows from mechanical and EHD air movers 219 and 220 are separated by a moveable gate 236 providing for selection of flow between the parallel air movers. For example, gravity can hold gate 236 in a downward position when mechanical air mover 219 is not operable and can be forced upward and open by operation of mechanical air mover 219, which in turn substantially blocks flow through EHD air mover 220 to prevent backflow from the higher-pressure, mechanically motivated air flow.

With reference to FIG. 4C, simultaneous parallel airflow may be provided by mechanical and EHD air movers 219 and 220 using distinct downstream ducting to prevent backflow from one into the other. Any number of various ducting or gating configurations or other suitable air flow control means may be used to limit back flow or otherwise control air flow through either or both of mechanical and EHD air movers 219 and 220.

With reference to FIGS. 5A-B, mechanical and EHD air movers 219 and 220 can be arranged in series. In FIG. 5A, EHD is located remote from outlet ventilation boundary 224 while mechanical air mover 219 is located closer to outlet ventilation boundary 224. In FIG. 5 b, mechanical air mover 219 is proximate inlet ventilation boundary 222, while EHD air mover 220 is closer to outlet ventilation boundary 224. In some implementations, the mechanical and EHD air movers 219 and 220 are proximate to each other and to one of the inlet and outlet ventilation boundaries 222 and 224. In some implementations, either or both of air movers 219 and 220 can be positioned to push or draw air along an air flow path.

In some implementations, a remote EHD may be positioned adjacent a dedicated inlet or adjacent an internal thermal source to control a localized enclosure skin temperature. Thus, any number of EHD air movers 220 may be used to enhance flow through a specific area of a system.

With reference to FIG. 6, EHD air movers 320 and mechanical air movers 319 may be used to motivate air through an internal plenum to provide system cooling and/or adjacent discrete components for component cooling. Thus, aspects of the invention may be applied to either or both of component cooling and general cooling within a given device or system. In the illustrated example implementation, a display device 300 includes laterally elongate arrays 350 including a plurality of discrete illumination sources, e.g., LEDs, constituting thermal point sources thermally coupled via one or more thermal spreader paths to an elongate set heat transfer surfaces 316. Arrays 350 are cooled by forced convection from one or more EHD air movers 320. EHD air movers 320 are illustrated adjacent both inlet and outlet ventilation boundaries. EHD air movers 320 can likewise be configured to more broadly motivate air, e.g., across a lateral extent of the display device or through an internal air plenum containing optical or electronic components generating heat. For example, a printed circuit board 304, e.g., with a central processing unit or graphics unit, is provided with forced convection cooling via one or more mechanical air movers 319. In some implementations, any combination of EHD air movers 320 and mechanical air movers 319 can provide forced convection cooling at a system level or to any number of particular thermal sources, including illumination sources, processors, power supplies and the like.

EHD air mover 320 is positioned and energizable to generate an air flow (indicated by arrows) to provide forced convective transfer of heat generated by the arrays 350, circuit board 304 or other system components to the environment. In some implementations, EHD air mover 320, or at least the cross-section of the air flow, is substantially coextensive in length with the elongate arrays 350. Of course, various heat spreaders, heat pipes, cooling fins, or other heat transfer structures and surfaces may be used in combination with EHD air mover 320 to effectively transfer heat away from the discrete illumination sources. For example, chassis 362 can be thermally conductive to conduct and distribute heat from the various supported components to be transferred to the air flow.

In some implementations, air flow may be spread across a substantial area of chassis 362 such that EHD air mover 320 serves to transport heat from the elongate array 350 and various other components thermally coupled to chassis 362. For example, an air flow inlet boundary 364 may be defined in a lower portion of a housing of display apparatus 300, and an outlet boundary may be defined in an upper portion of the housing such that the air flow (indicated by arrows) travels a major dimension of the display device 300. Thus, the inlet and outlet of the flow path may be positioned entirely outside of a rearward-most surface of the display housing. Alternatively, the flow path may extend between any number of the sides, top or bottom, front or back, and transition surfaces therebetween.

In some implementations, the air flow or flow path of the EHD air mover 320 may be generally confined to the thermal envelope of the elongate array 350, e.g., to an extreme upper or lower portion of the display housing. For example, elongate array 350 may be coupled via one or more thermal spreader paths to an elongate set of one or more heat transfer surfaces 316 spanning at least a substantial portion of the lateral extent of array 350. In some cases, EHD air mover 320 may motivate air flow over a relatively shorter flow path across the heat transfer surfaces 316. The inlets and outlets of the flow path can be defined in any suitable combination of display housing surfaces, e.g., front bezel portions, top or bottom surfaces, rearward or lateral surfaces.

In some cases, the air inlet and outlet may be defined such that air travels laterally along a top or bottom mounted elongate array 350 or vertically along a side-mounted elongate array 350. Air may be drawn in and rejected at any suitable location defined on a housing of the display device 300. For example, an inlet can be centrally located relative to the arrays 350 while the outlets are peripherally located relative to the arrays 350 or display area.

Any number of additional heat transfer surfaces or heat transfer structures may be provided, e.g., in the form of cooling fins, heat spreaders, and the like. In some implementations, it may be desirable to provide surfaces exposed to the air flow with an ozone reducing material, e.g., silver, to mitigate effects of any ozone produced by the EHD device or other components exposed to the air flow. Similarly, it may be advantageous to shield or otherwise protect various display apparatus components from ozone, e.g., an LCD display, diffuser, or other optically sensitive components. In some cases, the flow path is defined to confine air flow exposure to selected display apparatus components.

FIG. 7A is an illustrative side cross-sectional view of an integral computing display device having a tapered enclosure with a narrower edge-positioned EHD air mover and thicker inwardly positioned mechanical air mover. The enclosure presents a generally planar major surface with a substantial taper in thickness from a central portion toward a peripheral edge portion. In the illustrated configuration, the central portion accommodates electronics including heat sources such as processors, memory, etc.; although more generally heat sources may be distributed throughout the enclosure. Thickness toward the peripheral edge is substantially reduced such that less than about 10 mm of interior clearance (or perhaps 5 mm or less) is provided. Although mechanical air movers will not typically fit within such tight clearance, the illustrated elongate EHD air mover and array of heat sink fins can be accommodated.

During operation of the integral computing display device, passive cooling may initially be employed whereby convection causes air to rise upward from the illustrated heat sink fins and replacement air is drawn through a back mounted inlet ventilation boundary. Additional EHD motivated air flow may be added to silently assist. As will be understood, by energizing EHD emitter and collector electrodes, air flow is forced through the heat sink fins to provide forced convective cooling. As before, replacement air may be drawn through the illustrated back mounted inlet ventilation boundary. In addition, air may be drawn through the interior volume of the integral computing display device, e.g., from a bottom mounted inlet ventilation boundary (not specifically shown). Further, additional mechanically motivated air flow through the heat sink fins may be contributed by the fan illustrated within the central portion of the enclosure.

In some implementations, an EHD dedicated inlet can include a gate or valve to prevent back flow when a mechanical fan provides increased air flow along the flow path. In some implementations, an EHD air mover can selectively motivate air through a dedicated inlet or along an air flow path common to both air movers. Thus, the EHD air mover may be operated independently or in series or parallel with the mechanical air mover. In some implementations, the EHD air mover is wider than the mechanical air mover, and multiple mechanical air movers may be used to provide mechanical forced convection coextensive with the silent forced convection cooling of the EHD air mover. Alternatively, transition ducting can be used to accommodate any differences in dimensions between an EHD air mover and a mechanical air mover, e.g., an outlet cross-section can be up to 50 percent larger than a mechanical air mover cross-section.

With reference to FIG. 7B, an integral computing display device 200 includes forced convection cooling via both mechanical and EHD air movers 219 and 220 arranged in parallel and series for staged cooling. In the illustrated configuration, EHD device 220 spans substantially the entire width of display device 200. Dedicated EHD air mover inlets 222 are provided adjacent lateral portions of EHD air mover 220. A ducted air flow path traverses an internal plenum containing a mechanical air mover 219 motivating air over a heat pipe 214 connecting thermal sources 204 and 206 to heat transfer surfaces 216. A central portion of EHD air mover 220 is positioned within the ducted air flow path of mechanical air mover 219.

In some implementations, electronic system 200 operates in a first silent cooling state in which primarily passive cooling is sufficient, e.g., radiative and/or unforced convective cooling. For example, electronic system 200 may have limited thermal loading during a latent or standby mode. In a second silent cooling state, EHD air mover 220 provides forced convection cooling without the vibration or other acoustic emissions typical of a mechanical air mover. In a third cooling state, mechanical air mover 219 operates, with or without EHD air mover 220 at a lower capacity to prolong the perceived period of silent operation of electronic system 200, e.g., below 28 dBa. Operation of EHD air mover 220 in conjunction with mechanical air mover 219 can further extend the perceived period of silent operation. In a fourth cooling stage, mechanical air mover 219 is operated at a higher capacity in response to increased thermal loading while preferably still limiting mechanical noise to below 35 dBa. Lastly, in response to high thermal loading, mechanical air mover 219 can be operated at full capacity, still preferably below 40 dBa to preserve user comfort. Thus, EHD air mover 220 and mechanical air mover 219 may be operated independently and in combination to provide a perceived extended period of silent operation of electronic system 200.

In many EHD devices and other similar devices, detrimental material such as silica dendrites, surface contaminants, particulate or other debris may accumulate or form on electrode surfaces and may affect the performance, efficiency and lifetime of such devices. In particular, siloxane vapor breaks down in a plasma or corona environment and forms solid deposits of silica on the electrode, e.g., emitter or collector electrode. Others detrimental materials may build up on any number of electrode surfaces potentially causing decreased power efficiency, sparking or reduced spark-over voltage. Accordingly, in some EHD air mover implementations, an electrode cleaning mechanism is provided to mitigate detrimental material build-up.

With reference to FIG. 8, an EHD electrode cleaning mechanism 100 includes respective cleaning surfaces 102 and 104 positioned to frictionally engage at least a portion of a respective emitter electrode 106 and collector electrode 108. Cleaning mechanism 100 is moveable to cause respective cleaning surfaces 102 and 104 to travel in tandem along the respective surfaces of emitter electrode 106 and collector electrode 108 to thereby remove detrimental material such as silica dendrites, surface contaminants, particulate or other debris from the respective electrode surfaces. Cleaning surface 102 and 104 can be employed to remove detrimental material from electrodes 106 and 108 or to otherwise clean or condition the electrodes.

During cleaning of EHD electrodes, while the EHD air mover is powered off, speed of a mechanical air mover can be increased, e.g., to maintain system cooling capacity or to eject dislodged debris from the system. In some implementations, a separate air flow outlet may be provided for escape of dislodged debris to avoid build up of the dislodged debris on heat fins.

In some implementations, (not illustrated), additional cleaning surfaces can be provided to frictionally engage and travel over surfaces of the additional electrodes in tandem with travel of cleaning surfaces 102 along a longitudinal extent of emitter electrode 106. For example, in some implementations, a collector electrode 108 can be disposed upstream of the electrohydrodynamic fluid accelerator along the fluid flow path and can operate as an electrostatic precipitator.

While electrodes 106 and 108 are generally referred to as emitter and collector electrodes respectively, cleaning mechanism 100 may be used to clean any combination of electrodes, e.g., 106 and 108. While electrodes 106 and 108 are generally depicted as elongated or wire-type emitter and collector electrodes, any combination of electrode types and electrode surfaces may be cleaned individually or in tandem via cleaning surfaces 102 and 104 via movement of cleaning mechanism 100. For example, a first respective cleaning surface 102 may travel along a longitudinal extent of emitter electrode 106 and a second respective cleaning surface, e.g., cleaning surface 104, travels in tandem over a major dimension of a surface of collector electrode 108 or other electrode. For example, an ESP or EHD device can include grounding electrodes, repelling electrodes, backflow electrodes or other electrodes arranged to motivate air through the device to exhaust heat delivered, e.g., from a heat sink via a heat pipe.

Cleaning mechanism 100 can be driven or translated via a drive cable 110 trained about a drive pulley 112 and idler pulley 114, with drive pulley 112 being rotatable by a drive motor 116. Other types of drive mechanisms may be used to move cleaning mechanism 100 to thereby clean and/or condition an electrode. Cleaning cycles may be initiated as needed and performance checks conducted to determine sufficiency of electrode cleaning. For example, cleaning may be advantageously initiated as a function of time, detection of dendrite growth, or in response to various events, e.g., power cycles or electrode arcing.

With continued reference to FIG. 1B, dendrite material or other detrimental material may accumulate on the exterior of cleaning mechanism 100, e.g. adjacent cleaning surfaces 102 or 104 during cleaning and conditioning of electrodes 106 and 108. Accordingly, a secondary cleaning device, e.g., brush 126, is positioned near an end of the travel path of cleaning mechanism 100 to remove accumulated detrimental material from cleaning mechanism 100. Brush 126 is positioned to contact the cleaning mechanism exterior, e.g., leading edges or surfaces adjacent cleaning surfaces 102 and 104 where detrimental material dislodged from electrodes 106 or 108 may accumulate on cleaning mechanism 100. Thus, secondary detrimental material accumulation may be removed from cleaning mechanism 100 including cleaning surfaces 102 and 104 by brush 126 or other suitable secondary cleaning device.

In the particular illustrated implementation, brush 126 is positioned along an end portion of the path of travel of cleaning mechanism 100 and such that advancement of cleaning mechanism 100 against brush 126 causes brush 126 to deflect and to thereby wipe across the affected area of cleaning mechanism 100. The detrimental material dislodged by brush 126 can be accumulated in a receptacle area 128 positioned adjacent a stowed position where the cleaning mechanism 100 resides between cleaning cycles. Passages (not shown) in a sidewall or floor portion of receptacle area 128 can be provided to allow escape of the dislodged detrimental material from the system, for example, upon tipping of the system during transport or during operation of a mechanical air mover. Still in some implementations, passages are provided below the electrode wire such that dislodged detrimental material simply falls out of the electronic device, e.g., as a fine powder through vents in a lower surface. In some cases, receptacle area 128 may include a removable detrimental material bin.

Carbon is but one example of a conditioning material that may be present on cleaning surfaces 102 and 104. Other conditioning materials may be used, e.g., to provide ozone reducing coatings, sacrificial coatings, electrode surface refinishing, electrode lubrication, or other useful conditioning of electrodes. In some implementations, cleaning surfaces 102 and/or 104 include wearable, replaceable inserts retained on cleaning mechanism 100.

In some implementations, orthogonal or lateral travel of cleaning surface 102 serves to laterally deform electrode 106 as cleaning mechanism 100 travels a longitudinal extent of electrode 106 to further break up deposits of detrimental materials accumulated thereon. This lateral deformation can be in addition to other electrode deformation introduced in other directions, e.g., via a cleaning surface profile. In some cases, an elongated electrode may be bent or otherwise deformed in a first direction while being pulled or deformed in a second direction. Thus, an electrode may be subject to bending or deformation about two or more orthogonal axes.

Some implementations of thermal management systems described herein employ EFA or EHD devices to motivate flow of a fluid, typically air, based on acceleration of ions generated as a result of corona discharge. Other implementations may employ other ion generation techniques and will nonetheless be understood in the descriptive context provided herein. Using heat transfer surfaces, heat dissipated by electronics (e.g., microprocessors, graphics units, etc.) and/or other electronic system components can be transferred to the fluid flow and exhausted. Heat transfer paths, e.g., heat pipes, are provided to transfer heat from where it is generated within the internal plenum to a location(s) within the enclosure where air flow motivated by an EHD device(s) flows over heat transfer surfaces to dissipate the heat.

In some implementations, an EFA or EHD air cooling system or other similar ion action device may be integrated in an operational system such as a laptop, tablet or desktop computer, a projector or video display device, etc., while other implementations may take the form of subassemblies. Various features may be used with different devices including EFA or EHD devices such as air movers, film separators, film treatment devices, air particulate cleaners, photocopy machines and cooling systems for electronic devices such as computers, laptops and handheld devices. One or more devices includes one of a computing device, projector, copy machine, fax machine, printer, radio, audio or video recording device, audio or video playback device, communications device, charging device, power inverter, light source, medical device, home appliance, power tool, toy, game console, television, and video display device.

While the foregoing represents a description of various implementations of the invention, it is to be understood that the claims below recite the features of the present invention, and that other implementations, not specifically described hereinabove, fall within the scope of the present invention. 

1. An electronic system comprising: an enclosure having inlet and outlet ventilation boundaries; a flow path defined within the enclosure between the inlet and outlet ventilation boundaries; heat transfer surfaces thermally coupled to one or more thermal sources within the enclosure that, during operation of the electronic system, generate heat, the heat transfer surfaces introduced into the flow path to dissipate heat through passive cooling and forced convection cooling; an EHD air mover selectively operable to motivate air flow along the flow path for forced convection cooling of at least a portion of the heat transfer surfaces; and a mechanical air mover selectively operable to contribute to the air flow over at least a portion of the heat transfer surfaces.
 2. The electronic system of claim 1, wherein the EHD air mover is configured to provide forced convection cooling upon detection of a first performance threshold value, and the mechanical air mover is configured to provide active cooling upon detection of a second performance threshold value.
 3. The electronic system of claim 2, wherein the EHD air mover and mechanical air mover are both configured to provide forced convection cooling upon detection of a third performance threshold value.
 4. The electronic system of claim 2, wherein the first and second performance threshold values characterize at least one of a temperature, loading, output, and heat generation of the one or more of the plurality of electronic components.
 5. The electronic system of claim 1, wherein the EHD air mover and the mechanical air mover motivate air in series along the air flow path during joint operation.
 6. The electronic system of claim 1, wherein the EHD air mover and the mechanical air mover motivate air in parallel over respective heat transfer surfaces during concurrent operation.
 7. The electronic system of claim 1, wherein the EHD air mover is positioned upstream of the mechanical air mover and the mechanical air mover includes an ozone reducing material.
 8. The electronic system of claim 1, further comprising air flow gating moveable to provide a low impedance path during passive cooling and EHD air mover operation, at least in part, through other than the mechanical air mover.
 9. The electronic system of claim 1, further comprising ozone reducing material provided on a surface downstream of the EHD air mover relative to the air flow.
 10. The electronic system of claim 9, wherein the ozone reducing material is provided on at least one of the mechanical fan, heat transfer surfaces, surfaces exposed to an internal plenum, and ducting surfaces.
 11. An electronic system comprising: an enclosure having inlet and outlet ventilation boundaries; an EHD air mover disposed within the enclosure to motivate air flow along a flow path between the inlet and outlet ventilation boundaries; heat transfer surfaces thermally coupled to one or more thermal sources within the enclosure that, during operation of the electronic system, generate heat, the heat transfer surfaces introduced into the flow path downstream of the EHD air mover and including an ozone reducing surface treatment; and a mechanical air mover that is selectively operable to contribute to the air flow without, during periods when the mechanical air mover does not substantially contribute, substantially impeding the air flow over at least a portion of the heat transfer surfaces.
 12. The electronic system of claim 11, wherein flow restrictions otherwise imposed by the mechanical air mover during periods when the mechanical air mover does not substantially contribute to the air flow are mitigated by providing a low-speed idle power to the mechanical air mover.
 13. The electronic system of claim 11, wherein flow restrictions of the mechanical air mover are mitigated using a bypass path.
 14. The electronic system of claim 13, wherein the bypass path includes the EHD air mover.
 15. The electronic system of claim 11, operable in a passively ventilated mode, and wherein the flow path is oriented to, during passively ventilated operation of the electronic system, allow unforced convective air flow upward from the heat transfer surfaces, wherein draw of replacement air is substantially unimpeded by the mechanical air mover.
 16. The electronic system of claim 15, wherein in the passively ventilated mode, the unforced convective flow is drawn primarily through the EHD air mover rather than the mechanical air mover.
 17. The electronic system of claim 11, wherein the mechanical air mover precedes the EHD air mover in the flow path.
 18. The electronic system of claim 11, wherein the mechanical air mover follows the EHD air mover in the flow path and includes an ozone reducing surface treatment on at least one of the air mover housing and the air mover blades.
 19. The electronic system of claim 11, further comprising: a valve that merges respective air flow contributions of the mechanical air mover and the EHD air mover.
 20. The electronic system of claim 11, wherein the EHD air mover and the mechanical air mover direct respective air flows over separate portions of the heat transfer surfaces.
 21. An electronic system comprising: an enclosure having inlet and outlet ventilation boundaries; and an EHD air mover and a mechanical air mover, each selectively operable and each disposed within the enclosure to motivate air flow along a flow path between the inlet and outlet ventilation boundaries; a unitary set of heat transfer surfaces thermally coupled to one or more thermal sources within the enclosure that, during operation of the electronic system, generate heat, wherein air flow from the EHD air mover traverses a first subset of the heat transfer surfaces and wherein air flow from the mechanical air mover traverses a second subset of the heat transfer surfaces at least partially distinct from the first subset.
 22. The electronic system of claim 21, wherein the first and second subsets exhibit at least one of dissimilar fin pitch, dissimilar fin depth, dissimilar fin height, dissimilar fin material, dissimilar thickness, dissimilar angle of attack and dissimilar leading or trailing edge profile.
 23. The electronic system of claim 21, wherein the first and second subsets present dissimilar traversal length to respective air flows.
 24. The electronic system of claim 21, operable in a passively ventilated mode, and wherein the flow path is oriented to, during passively ventilated operation of the electronic system, allow unforced convective air flow upward through at least the first subset of the heat transfer surfaces, wherein draw of replacement air is substantially unimpeded by the mechanical air mover.
 25. The electronic system of claim 24, wherein in the passively ventilated mode, the unforced convective flow is drawn primarily through the EHD air mover rather than the mechanical air mover.
 26. An electronic system comprising: an enclosure having inlet and outlet ventilation boundaries; a flow path defined within the enclosure between the inlet and outlet ventilation boundaries; heat transfer surfaces thermally coupled to one or more thermal sources within the enclosure that, during operation of the electronic system, generate heat, the heat transfer surfaces introduced into the flow path to dissipate heat through passive cooling and forced convection cooling; an EHD air mover selectively operable to motivate air flow along the flow path for forced convection cooling of at least a portion of the heat transfer surfaces; and a mechanical air mover selectively operable to contribute to the air flow over at least a portion of the heat transfer surfaces; wherein the electronic system is operable in a first silent cooling state characterized primarily by passive cooling; wherein the electronic system is further operable in a second silent cooling state in which the EHD air mover provides forced convection cooling; wherein the electronic system is further operable in a third cooling state in which the mechanical air mover operates, with or without EHD air mover, at a lower capacity to provide nearly silent forced convection below about 35 dBa; and wherein the electronic system is further operable in a fourth cooling state in which the mechanical air mover is operable at a higher capacity to provide forced convection cooling below about 40 dBa.
 27. The electronic system of claim 26, wherein forced convection cooling in the second silent cooling state is performed at below about 20 dBa.
 28. The electronic system of claim 26, wherein forced convection cooling in the third forced convection cooling state is performed at below about 28 dBa.
 29. An electronic system comprising: an enclosure that exhibits a generally planar major surface with a substantial taper in thickness from a central portion thereof toward one or more peripheral edge portions thereof; an elongate set of heat transfer surfaces thermally coupled to one or more thermal sources within the enclosure that, during operation of the electronic system, generate heat; an EHD air mover operable to motivate air flow along a flow path that traverses the elongate set of heat transfer surfaces and out through an outlet ventilation boundary of the enclosure; and a mechanical air mover selectively operable to boost air flow through the EHD air mover along the flow path that traverses the elongate set of heat transfer surfaces and out through the outlet ventilation boundary, wherein the EHD air mover and the elongate set of heat transfer surfaces are positioned within the enclosure proximate at least a first one of the peripheral edge portions wherein the substantial taper provides no more than about 10 mm of thickness, and wherein the mechanical air mover is displaced from the EHD air mover and the elongate set of heat transfer surfaces at a position within the enclosure wherein thickness is at least two times (2×) that at the first peripheral edge portion.
 30. The electronic system of claim 27, wherein the electronic system includes a display, and wherein orientation of the electronic system during operation places the first peripheral edge portion upward such that the flow path through the EHD air mover and the elongate set of heat transfer surfaces is generally vertical.
 31. The electronic system of claim 30, wherein the thermal sources include one or more processors of the electronic system positioned within the central portion.
 32. The electronic system of claim 27, operable in a passively ventilated mode, and wherein the flow path is oriented to, during passively ventilated operation of the electronic system, allow unforced convective air flow upward through the elongate set of heat transfer surfaces, wherein draw of replacement air is through EHD air mover.
 33. The electronic system of claim 27, wherein the EHD air mover and the elongate set of heat transfer surfaces are positioned within the enclosure proximate at least a first one of the peripheral edge portions wherein the substantial taper provides no more than about 5 mm of thickness.
 34. A method of forced convection cooling comprising: energizing an EHD air mover disposed within an enclosure to motivate air flow along a flow path between inlet and outlet ventilation boundaries of the enclosure; reducing power to the EHD air mover for cleaning operations; cleaning one or more electrodes of the EHD air mover; and augmenting air flow provided by a mechanical air mover during the cleaning.
 35. The method of claim 34, wherein the augmented air flow discharges from the enclosure material removed from the one or more electrodes of the EHD air mover.
 36. The method of claim 34, wherein the augmented air flow provided by the mechanical air mover is of a substantially similar flow rate to combined air flow provided during operation of both the EHD air mover and the mechanical air mover.
 37. The method of claim 34, wherein cleaning is performed by at least one of heating, vibrating, and frictionally engaging the electrode. 